This is more of a task than a clear-cut bug but I wanted to track this so I don't forget.

We recently added support for opaque tokens, but in order to support Google as an IDP we should check if toolhive supports their introspection format - my guess is that the answer will be "no". Looking at https://cloud.google.com/docs/authentication/token-types it seems that the fields are different from RFC 7662. Since we are interested in Google access tokens ourselves, we should test and make sure they work.